MACROMEDIA ClusterCATS, Руководство пользователя

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30 Chapter 2 Scalability and Availability Overview
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There are no recurrent licensing fees
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It is semi-intelligent; routers can load balance in a round-robin fashion, detect
failures, redirect traffic, and remove failed servers from a cluster.
Note: Load-balancing devices offer different features and capabilities.
Considerations
Carefully evaluate the following issues against a router’s attributes:
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Expense — hardware devices can be expensive relative to some software solutions,
even without yearly licensing fees.
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Single point of failure — if a problem develops on the load-balancing device itself and
it fails, your load-balancing and failover strategies do not work. Although some
load-balancing devices come with secondary systems for this reason, this additional
equipment often inflates the overall price of a hardware solution.
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Lack of application-awareness — the device cannot be tuned for particular types of
web applications (static vs. dynamic sites) or for the development tools used to build
them (scriptlets vs. JSP vs. CGI vs. ASP and so on). Consequently, a router cannot
measure the performance of a web application server.
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Limited intelligence — the device does not let you configure individual load and
redirection thresholds for each server in a cluster, so it cannot effectively manage load
to prevent failures.
Software-based clustering solutions
There are several kinds of software-based clustering solutions on the market. As with
hardware-based clustering solutions, there are strengths and weaknesses associated with
each. These software solutions include:
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Round-robin DNS — a very popular choice because of its relative simplicity and low
implementation cost, but does not include intelligence for load balancing or failover.
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Primary/backup clustering — cloned systems provide redundancy for one another.
This type of clustering does not provide parallel server load balancing.
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Smart clustering — combines the advantages of round-robin DNS and backup
clustering to provide simplicity with intelligence and redundancy.
ClusterCATS lets you easily create, optimize, and maintain “smart” clusters to support
your web applications. ClusterCATS runs on Windows, Solaris, and Linux platforms and
works with leading mission-critical web servers, including Microsoft IIS, Netscape
Enterprise Server, and Apache. It is easily administered from remote locations and
provides robust features, including:
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Configuring load and redirection thresholds by server
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Optimizing the load-balancing scheme with application-aware and session-aware
load balancing
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Automatically detecting failures
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Automatically redirecting traffic to available servers
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Automatically notifying administrators of problems